DESCRIPTION: Various energy sources have been used to "ablate" (coagulate and/or vaporize) myocardium responsible for initiating or sustaining ventricular tachycardia. We propose to develop a novel catheter system that initially detects the location responsible for the arrhythmia and subsequently treat the area with an interstitial dose of diffused laser diode energy. Lasers have not been widely used to treat arrhythmia due to the high cost an complexity of the laser source and lack of a laser catheter capable of creating a reproducible tissue response without directly radiating blood, forming coagulum or perforating the heart. The proposed technologies overcome these deficiencies. Experiments are proposed that will allow better understanding of the effect of laser diode radiation on myocardium, observe the arrhythmic response to said radiation, and assessment of the healing process of these lesions for size, histology and proarrhythmic potential. An innovative catheter will be designed, constructed and tested that will allow electrophysiologic monitoring with subsequent ablation when the area responsible for the tachycardia is located. This coagulation will be induced interstitially be inserting a diffusing tip fiber intramyocardially. The diffusing tips spread light out in a cylindrical pattern which has advantages over bare end fibers currently being used.